The present invention generally relates to filters for removing particulates from the exhaust gas of diesel engines, and deals more particularly with a method of regenerating the filter only when the level in the engine""s fuel tank is above a preselected value.
Emission after-treatment devices are used to collect particulate matter from the exhaust gas of internal combustion engines. In particular, conventional emission treatment devices for diesel engines include particulate filters, oxidation catalysts and nitrous oxide (NOx) catalysts. A problem exists with particulate filters in that the particulates, which consist largely of carbon particles, tend to plug the filters, resulting in a restriction to the flow of exhaust gas. In order to periodically regenerate or purge the filter from particulates, it is known to take measures which result in an increase of the exhaust gas temperature above a predetermined level (e.g. above (450xc2x0 C.) in order to incinerate the carbon particles accumulated in the filter.
One conventional method used to increase the exhaust gas temperature involves controlling a throttle valve in the intake manifold of the engine. In particular, it is known that by throttling/closing the throttle valve, the exhaust gas temperature may be increased. Numerous methods have been used for controlling the throttle valve. For example, in one conventional method, the intake throttle valve is controlled by utilizing the difference between a calculated target intake manifold pressure, and an actual intake manifold pressure. The target intake manifold pressure is calculated using an engine speed and engine load. The regeneration process is scheduled by engine control software based on an estimate of the particulate loading. Known techniques for raising the exhaust gas temperature result in an increase in the fuel consumption during the regeneration process. Driver dissatisfaction can result, however, if the regeneration event is initiated at a time when the vehicle""s fuel tank is near empty, as when the low fuel warning lamp is illuminated. For example, the driver may observe an unexpected rapid reduction in the vehicle""s remaining driving range at a critical time, or the driver may observe what appears to be poor fuel economy due to the driver""s closer scrutiny of fuel mileage when the fuel tank is near empty. In an extreme case, the higher fuel consumption may result in the vehicle running out of fuel before it reaches the next refueling station.
Thus, there is a need for a method of regenerating diesel engine particulate filters only above low fuel levels in order to obviate the problems mentioned above.
The present invention provides a method of regenerating a diesel particulate exhaust gas filter only when the supply of fuel for the diesel engine is above a predetermined value.
According to one aspect of the invention, a diesel exhaust filter regeneration method is provided, comprising the steps of sensing when the level of diesel fuel in a fuel tank of a vehicle is below a first threshold level representing a relatively low fuel level; regenerating the filter; and inhibiting the regeneration of the filter when the sensed fuel level is below the threshold value. The method further optionally includes sensing when the fuel level is below the first threshold, and a second, higher threshold level; sensing when the particulate loading of the filter is between a first relatively high load level, and a second load level higher than the first load level; and, regenerating the filter when the sensed fuel level is between the first and second threshold levels, and the sensed loading level of the filter is between the first and second load levels. The filter is regenerated by determining when the loading level of particulates in the filter exceed a predetermined loading level, and increasing the temperature of the exhaust gas to at least a pre-selected exhaust temperature above which the filter is regenerated through the oxidation of the particulates. The exhaust temperature is maintained above the pre-elected temperature for a predetermined length of time corresponding to a desired level of filter regeneration. The increase in exhaust gas temperature may be achieved by a number of techniques, including throttling the engine intake by reducing the oxygen content in the exhaust gases, by closing an ERG valve of the engine or by performing pilot injection of fuel into the engine""s cylinders.
According to another aspect of the invention, a method of controlling the regeneration of a diesel particulates in the exhaust filter for a diesel fuel engine is provided, comprising the steps of inhibiting the regeneration of the filter when the level of fuel in a fuel tank of the vehicle is below a first threshold level and a second higher threshold level, and the particulate loading of the filter is between a first, relatively high load level and a second load level higher than the first load level in which regeneration of a filter would ordinarily be necessary.
Accordingly, it is the primary object of the present invention to provide a method of regenerating a diesel exhaust gas particulate filter which avoids a regeneration when the fuel supply to the engine is at a relatively low level.
Another object of the invention is to provide a method as described above which initiates a filter regeneration event only if the filter load is above a predetermined level.
Another object of the invention is to provide a method of the type mentioned above which reduces the possibility of a diesel engine powered vehicle running out of fuel as the result of increased fuel consumption at low fuel levels due to the initiation of a filter regeneration event.
A still further object of the invention is to provide a method of the type mentioned above which reduces driver dissatisfaction as a result of the effects of particulate filter regeneration during low fuel levels.
These, and further objects and advantages of the present invention will be made clear or will become apparent during the course of the following description of a preferred embodiment of the invention.